Abstract

Abstract

A study was made to evaluate the movement of nutrient elements in rainwater percolating through a well-drained Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) forest soil. Radiotracers of phosphorus, potassium, and calcium, mixed with stable elements, were applied to the forest floor simulating rainwash input. Leachates from tension lysimeters were collected periodically and analyzed for nutrient and tracer contents. Trees and soil were sampled and analyzed at the end of the experimental period. The data showed large coefficients of variation typical of biological materials. Twenty percent of the labeled phosphorus leached through the forest floor during the year, representing 10% of the total phosphorus movement with rain water. Similarly, 8% of labeled potassium, representing 27% of leached potassium, and 2% of labeled calcium, representing 5% of leached calcium, moved annually with rain water through the forest floor. Comparable leaching values through the top 20 cm of mineral soil were a thousand times less, but with most of calcium and least of phosphorus released. These data were related to forest soil contents and indicated the elemental mobility to be dependent on the physico-chemical properties of the forest soil, as well as the ionic properties and biological functions of the nutrient elements.

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